1) Field of the Invention
The present invention relates to a method for producing a ceramic sintered article from a batch material containing a plasticizing medium generally being water; and a method for molding ceramic, wherein a ceramics batch containing water and an organic binder is poured into a batch-retaining portion and held once therein, and then the batch is injected into an impermeable die under pressure, a part of the molding surface of which impermeable die is constituted with a material having a contact angle with water of at least 80 degrees; and a molding apparatus to be used in the molding method.
2) Related Art Statement
There have hitherto been known a slip casting method or injection molding method as a molding method for producing ceramic structural parts, such as a turbine wheel and the like, having a complicated shapes.
The slip casting method is a method, wherein a slurry of ceramic powder is poured into a casting die made of gypsum or the like, and solidified therein to obtain a shaped article. In the cast molding method using a gypsum die or the like, a shaped article having a complicated shape can be produced, but the shaped article often has poor dimensional accuracy due to the poor accuracy of the die. Moreover, a long molding time is generally required due to the use of a large amount of water as a plasticizing medium.
A pressure cast molding method is a method for producing a shaped article, wherein a slurry of ceramic powder is poured into a permeable casting die, the slurry is pressed to exhaust a large amount of water through the permeable casting die, and to solidify the slurry. In this method, a shaped article having a complicated shape can be produced, but the shaped article has poor retention, and it is difficult to release the shaped article from the die, and hence a long molding time is required.
The injection molding method is a method, wherein a homogeneous mixture of ceramic powder with various thermoplastic organic binders is heated, and then the mixture is injected into a die and cooled therein to obtain a shaped article. In this injection molding method, a shaped article having a complicated shape can be produced. Further, this method is adapted to the mass production of shaped articles. However, the shaped article must be heated for a long period of time of generally at least 100 hours in order to prevent the shaped article from being cracked or deformed during the removal step of organic binder, that is, during the degreasing step. Moreover, this injection molding method has been used only in the production of a shaped article having a small wall thickness.
Japanese Patent Laid-open Specification No. 61-10,405 discloses a method, wherein a slurry consisting of a mixture of fine ceramic powder, such as Al.sub.2 O.sub.3, SiC, Si.sub.3 N.sub.4, ZrO.sub.2 or the like, water and an organic additive is subjected to an injection molding to produce a shaped article. However, in this method, a particular porous die is used, and a pressure is kept to 100-600 kg/cm.sup.2 after injection, whereby water is removed from the slurry to obtain a green shaped article. Therefore, a complicated operation must be carried out in order to remove the green shaped article from the die.
The conventional compression molding method or transfer molding method carried out in the production of ceramic shaped articles is relatively simple in the operation, but has been used only in the production of small and thin-wall articles, such as chinawares and the like, and has not been used in the production of the above described structural parts, such as turbine wheels and the like, having complicated shapes.
The present invention aims to eliminate the drawbacks of the above described conventional techniques, and to decrease significantly the production steps and the production time in a method for producing a ceramic sintered article, wherein a shaped article is produced through an injection molding, transfer molding or the like, water and organic binder are removed from the shaped article, and then the shaped article is fired; and further to provide a method capable of producing monolithically a thick-wall sintered article, such as a a turbine wheel and the like, having a complicated shape illustrated in FIG. 2 through an injection molding, compression molding or transfer molding. In order to attain these objects, the inventors have made various investigations for the production of a thick-wall sintered article having a complicated shape by a method, wherein a ceramic batch containing a plasticizing medium generally being water which is not used in the conventional methods, and further containing an organic binder as a plasticizer, is formed into a shaped article having a complicated shape through an injection molding, compression molding or transfer molding, and the shaped article is fired. As a result, the inventors have reached the present invention.